The Feyenoord coach heaped praise on the young Sweden international, and believes he has the potential to emulate the AC Milan striker
The Sweden international impressed during his one-year loan spell at Feyenoord in the 2011-12 campaign, and Koeman had nothing but praise for the youngster.
"I think that John can be as good as Zlatan Ibrahimovic," Koeman said to Voetbal International.
"I've coached them both. Zlatan struggled a lot more than John to find his way in Netherlands. John is on the same level as players such as Wesley Sneijder and Rafael van der Vaart at that age.
"That's great for a striker, because it's a very difficult position.
"He arrived at the club and immediately adapted to his new surroundings, even though I don't think he had ever played in a formation with three attackers before.
"If you're capable of that at the age of 19, and can be this important for a team, you're going to become a big player. Simple as that."
Guidetti netted 20 goals in 23 Eredivisie appearances in 2011-12.
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